A problem with therapeutically active substances is that these compounds cannot be administered by every administration route at the same dosage level with the same resulting activity. Various substances which can be injected show a considerable loss of activity on oral administration. Other substances, which can be orally administered, lose bioavailability to a considerable extent if they are rectally administered.
Oral administration forms are particularly problematical in those patients who tend to vomit. This problem is apparent with therapies such as immunosuppression or candidiasis of the oesophagus.
Administration in the form of injections is not appropriate in many cases. Many people have a fear of frequent injections and with cachectic patients injection is difficult. The present invention is therefore intended to provide rectally administered pharmaceutical compositions which have approximately the same bioavailability of active component as oral administration forms.
In order to achieve the same high blood level values as after an oral dose, approximately a 1.5 to 3 to fold amount of the oral dose must be incorporated in the suppository (H. Sucker, P. Fuchs and R. Speiser, Pharmazeutishe Technologie (Pharmaceutical Technology), Georg Thieme Verlag, Stuttgart 1978). The problem of incorporating a substantially higher amount of the active compound is that absorption can differ greatly from person to person and in the case of good absorption a blood level value is achieved which is clearly above the optimum blood level value.
It is therefore the object of the present invention to make available a pharmaceutical composition for rectal administration which has approximately the same bioavailability as an oral administration form.